365 Nights of Astronomy

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Altair, the Last of the Summer Stars

Summer is slowly cooling off in the northern hemisphere but many of its brightest stars can still be easily seen in the evening sky. Especially prominent is the Summer Triangle, made up of Vega, Deneb and Altair.

Altair is the brightest star in the constellation of Aquila, the Eagle and as the most southerly member of the Summer Triangle, it’s also the last to rise in northern hemisphere skies.

The twelfth brightest star in the sky and, at just under 17 light years away, one of the closest, it’s been a popular star across the world for centuries. In Asian legends it represents the cow-herder who fell in love with a princess (Vega). The Milky Way represents the river that keeps the star-crossed lovers apart.

Image Credit: NASA/JPL/Caltech/Steve Golden

In reality, the star is nearly twice as massive as the Sun, is eleven times as luminous and rotates once on its axis every nine hours. This rapid rotation causes the star to bulge at its equator so that it loses its spherical shape and morphs into an ellipsoid instead.

If you want to catch Altair and the Summer Triangle, take a look at about 9 p.m. tonight when they’ll be overhead. As the days go by and the seasons change, the stars will rise and set earlier. Wait another month and look again at 9 p.m. – where are the summer stars now that the autumn is upon us?

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